Directional antenna with conical scanning



Dec. 9, 1958 J. L. BUTLER DIRECTIONAL ANTENNA WITH CONICAL SCANNING 2 Sheets-Sheet 1 Filed April 22.

Fig. 2

Jesse L.Butler INVENTOR.

N Afiorney Dec. 9, 1958 J. BUTLER DIRECTIONAL ANTENNA WITH CONICAL SCANNING I 2 Sheets-Sheet 2 Filed April 22. 1954 RIGHT LEFT DOWN

Jesse L.Butler INVENTOR.

Attorney United States Patent DIRECTIONAL ANTENNA WITH CONICAL SCANNING Jesse L. Butler, Nashua, N. H., assignor, by mesne assignments to Sanders Associates, Incorporated, Nashua, N. H., a corporation of Delaware Application April 22, 1954, Serial No. 424,893

7 Claims. (Cl. 343756) The present invention relates to the art of radiating electromagnetic energy. More particularly, this invention relates to conical scanning antenna systems as used in radar.

In the prior art many systems have been proposed for developing a conical beam of electromagnetic energy by causing beam rotation about the axis of the antenna system. This beam rotation is familiarly termed conical scanning in the art, and is to be distinguished from the azimuth and elevation scanning functions of the system as a whole.

Conical scanning systems as developed in the prior art are characterized by essentially unbalanced mechanical rotational systems. The speed of the scanning required by modern radar techniques is unattainable by such systerns.

It is therefore an object of the present invention to provide an improved antenna system providing high speed conical scanning.

It is a further object of the present invention to provide a conical scanning antenna system that is electrically and mechanically balanced.

A still further object of the present invention is to provide an improved conical scanning antenna system that is especially reliable in operation.

Other and further objects of the invention will be apparent from the following description of a typical embodiment thereof, taken in connection with the accompanying drawings.

In accordance with the invention, there is provided an antenna system. Included in the antenna system is a combination of a source of plane-polarized, electromagnetic energy characterized by an electric vector having a predetermined direction of polarization, a shaft, and a means for rotating the shaft. A radiating means responsive to the energy is coupled to the source and carried by the shaft. The radiating means comprises three radiating elements arranged substantially in the form of an equilateral triangle.

In the accompanying drawings:

Fig. 1 is a schematic diagram illustrating conical scanning as provided by the present invention;

Fig. 2 is a side view of a preferred embodiment of the present invention;

Fig. 3 is an enlarged, detailed end view of a portion-of the embodiment in Fig. 2; and

Fig. 4 is a series of schematic diagrams illustrating the operation of this invention.

Referring now in more detail to the drawings and with particular reference to Fig. 1, an antenna system indicated at 1 is depicted as radiating a beam 2 of electromagnetic energy as shown. The main axis 3 of the beam is caused to rotate about the antenna system axis or boresight axis 4, as shown. The rotating or circular motion of the beam axis 3 is illustrated by the path 5. The extreme lower position of the beam is illustrated by the phantom lines 6. This rotation of the beam thus provides what is known as conical scanning.

Referring now more particularly to Fig. 2, the antenna of the present invention comprises a primary radiator 7 (for example, a rectangular waveguide which inherently efiects a plane polarized mode of propagation of the electromagnetic energy) developing a beam of electromagnetic energy for the system. A transmitter 16, coupled to the primary radiator 7, provides a source of electromagnetic energy. A secondary radiator 8, hereinafter termed tripole radiator, is provided as shown. A shaft 9, mechanically coupled to the radiator 8, is rotated by a motor 10. A paraboloid reflector 11 is provided in the position shown so as to reflect the energy radiated by the radiator 8 to form a beam in the direction indicated at 12. The reflector 11 it attached to and supported by the waveguide 7 and a support rod 17. The radiator 8 comprises a plastic disk portion 13, see Fig. 3, to which are affixed metallic radiating elements 14 substantially in the form of an aquilateral triangle as shown. The elements 14 are chosen to be one-half wave long at the operating frequency range, for example 3 centimeters at 5 kilomegacycles.

The operation of the system can be better understood with particular reference to Fig. 4. Electromagnetic energy, plane polarized (by virtue of the rectangular waveguide) such that its electric vector 15 is vertical as shown, is fed to the tripole radiator. A dipole (half-wave length) element radiates a maximum amount of energy when it is parallel to the electric vector and a minimum or sub stantially zero, when it is perpendicular to the electric vector. In particular, such an element radiates energy in accordance with the expression:

W=k cos 0 In the above expression: W equals the electromagnetic energy radiated by the dipole having an electric vector parallel to the electric vector 15; k equals a constant and 6 is the angle between the dipole element and the electric vector 15.

Of particular significance in the present invention is the characteristic of the tripole radiator whereby a single rotation through 360 degrees effects three rotations of the resultant beam of energy. In the diagram (a), the tripole is schematically illustrated by the dipole elements A, B, and C, positioned such that the angles between them equal 60 degrees as shown. The element A is positioned at 0 degrees with respect to the electric vector 15 and therefor radiates k units of energy. Since the center of radiation of the element A is to the right of the common center 0, the main axis of a beam radiated by element A is displaced to the right of the center 0. The element B is displaced from the electric vector 15 by 300 degrees, hence its center of radiation is to the left of the center 0 by less than a maximum amount. Furthermore, in accordance with the expression for W above, the element radiates only .25k units of energy. Similarly, the element C is displaced from the electric vector 15 by 240 degrees and accordingly radiates .25k units of energy.

The centers of radiation of the elements B and C are equally disposed about the horizontal axis of the radiator, therefore, there exists no tendency for the main axis of the resultant beam to be deflected up or down. It is clear, however, that the resultant beam of the radiator is deflected to the right since the radiation centers are not equally disposed about the vertical axis. In addition, the element A in accordance with the expression for W above is controlling since it radiates a total amount of energy equal to k; whereas, the energy in the resultant beam radiated by the elements B and C is only .Sk units of energy. The total amount of energy thus radiated is equal to 15k units of energy.

In the diagram (b), the element A has been rotated 30 degrees. The energy radiated by element A is then equal to .75k units of energy. The element B is displaced from the electric vector 15 by 30 degrees and also radiates .75k units of energy. The element C is precisely perpendicular to the electric vector 15 and radiates substantially zero energy. The main aXis of the resultant beam is deflected down, since the radiation centers of the elements A and B are disposed below the horizontal axis of the radiator. Again, the total amount of energy radiated is equal to 1.5 k units of energy.

In the diagram the element A has been rotated 60 degrees with respect to the electric vector 15. The element B is precisely parallel to the electric vector 15, and accordingly radiates k units of energy. The radiation center of the element B is left of the center 0. The elements A and C radiate a total of .Sk units of energy with a resultant radiation center to the right of the center 0 less than a maximum amount. Since the element B is controlling, the main axis of the resultant beam will be deflected left.

In the diagram (d), the element A is shown rotated 90 degrees with respect to the electric vector and radiates no energy. The elements B and C radiate a total of 1.5k units of energy and their radiation centers are displaced above the center 0; hence, the resultant beam is displaced up as shown at 3 in Fig. 1. In the diagram (2), the element A is shown rotated 120 degrees with respect to the vector 15. The element C is now positioned such that the operation of the system as described with respect to the element A above is repeated.

In the diagram (f), the locus of the main axis of the resultant beam due to the rotation of the tripole radiator through an angle of 120 degrees is illustrated. The points W, X, Y, and Z relate to the positions as illustrated by the diagrams (a), (b), (c), and (d), respectively. By this analysis, it is clear that the main axis of the beam rotates through 360 degrees three times while the tripole radiator mechanically rotates through 360 degrees once.

From the above description it is to be noted that the system as described is inherently electrically and mechanically balanced. The tripole radiator may be readily fabricated in accordance with typical etched circuit or printed circuit techniques. Since the motor, shaft, and tripole radiator may be very light and are mechanically balanced, the physical speed of rotation may be so increased that conical scanning rates may be increased from a typical value of 50 cycles per second to as high as 1,000 cycles or more per second.

The present invention greatly enhances the effectiveness of modern radar techinques as used in the detection and control of supersonic aircraft.

While there has been hereinbefore described what is at present considered a preferred embodiment of the invention, it Will be apparent that many and various changes and modifications may be made with respect to the embodiment illustrated, without departing from the spirit of the invention. It will be understood, therefore, that all those changes and modifications as fall fairly within the scope of the present invention, as defined in the appended claims, are to be considered as a part of the present invention.

What is claimed is:

1. In a conical scanning antenna system, the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a radiating means having three radiating elements arranged substantially in the form of an equilateral triangle; means directing said polarized energy through said radiating means, with its plane of polarization parallel to the plane of said elements; and means for rotating said radiating means relative to said energy and producing, thereby a resultant conical scanning beam at three times the frequency of rotation of said radiating means.

2. In an antenna system, the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a shaft; means for rotating said shaft; and a radiating means coupled to said scurce and responsive to said energy and carried by said shaft, said radiating means comprising three radiating elements arranged substantially in the form of an equilateral triangle.

3. In an antenna system, the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a disk; means for rotating said disk; and a radiating means coupled to said source and responsive to said energy and carried by said disk, said radiating means comprising three radiating members being arranged substantially in the form of an equilateral triangle in a plane substantially perpendicular to the direction of propagation of said energy.

4. In an antenna system, the combination of a source of electromagnetic energy; a primary radiating means coupled to said source for providing a beam of planepolarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a rotatable shaft; and a secondary radiating means coupled to said primary radiating means and responsive to said energy and carried by said shaft, said secondary radiating means comprising three radiating members arranged substantially in the form of an equilateral triangle and adapted to re-radiate energy received from said primary radiating means.

5. In an antenna system, the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a shaft; a radiating means coupled to said source and responsive to said energy and carried by said shaft, said radiating means comprising three radiating members arranged substantially in the form of an equilateral triangle; and reflector means disposed adjacent said radiating means and adapted to reflect the radiated energy in the form of a beam.

6. In an antenna system, the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a parabolic reflector; a rotatable shaft carried by said reflector along its central axis; a radiating means coupled to said source and responsive to said energy and carried by said shaft, said radiating means being positioned at the focal point of said reflector and comprising three radiating elements distributed substantially in the form of an equilateral triangle in a plane substantially perpendicular to the direction of propagation of said energy.

7. In an antenna system, the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; rotary supporting means; means for rotating said supporting means; and a radiating means coupled to said source and responsive to said energy and carried by said rotary supporting means, said radiating means comprising three radiating elements arranged substantially in the form of an equilateral triangle.

Heintz Nov. 14, 1933 Guanella Mar. 3, 1953 

